1. Field of the invention
This invention relates to a fuel cell system and, more particularly, to a means for forming a seal between a fuel cell stack and manifolds to be fixed to respective sides of the fuel cell stack.
2. Description of the Prior Art
In a fuel cell system, manifolds are sealingly fixed to sides of a fuel cell stack with bolts. Sealing members are sandwiched between the peripheries of the sides of the fuel cell stack and flanges of the manifolds to form a seal between them. However, the manifolds are fastened only at their upper and lower portions of the flange to the sides of the top and bottom plates of the stack with the bolts. Thus, it is difficult to avoid unevenness of fastening force acting on the sealing member. For this reason, the sealing members extending in the stacked direction of the fuel cell units may loose their sealing function, resulting in a leakage of the gas from the manifolds.
To solve this problem, one of the inventors of the present invention, H. Hagino has proposed together with H. Ide and Y. Miyake, in Japanese patent application laid-open No. 58-197679, to use rigid frames 3 for sealingly fixing manifolds 9 to sides of the fuel cell stack 1, as shown in FIGS. 3 and 4. In such fuel cell system, the fuel cell stack 1 is provided with sealing members 2 at peripheries of its sides and tightly fastened by rigid frames 3 interconnected by bolts 4 and strips 5 mounted at their sides. When assembling this system, bolts 4 fixed at one end of the sides of the frame 3 are engaged at the other end with strips 5 mounted on one side of the adjacent frame 3 and fastened with a spring 6 and a nut 7. The manifolds 9 are sealingly fixed to the frames 3 with screws 10. Arranged between the frames 3 and the manifolds 9 are gaskets 8 to form a seal between them. Since the fuel cell stack 1 is uniformly fastened by the frames 3, a uniform force is applied to every part of the sealing members 2. Also, a uniform force is applied to every part of the gaskets 8 since the manifolds is fastened at its flange with screws along its whole circumference. Thus, it is possible to prevent a leakage of the gas from the system.
However, in such a construction is troublesome to assemble the fuel cell system since the bolts 4 mounted on the sides of one frame must be engaged with strips 5 mounted on the sides of the adjacent frame 3. Also, if any strip or bolt is damaged, it is impossible to tighten the frames uniformly, making it difficult to achieve the uniform and complete sealing between the fuel cell stack 1 and the frame 3. This results in the lowering and ununiformity in the fuel cell characteristics. In addition, the strips and bolts have a realatively long length, so that they cause disadvantages in the system design and in size.
Accordingly, it is an object of the present invention to provide a fuel cell system which overcomes the aforesaid disadvantages.
Another object of the present invention is to provide means for forming a seal between a fuel cell stack and manifolds to be fixed to sides of the fuel cell stack.